The present invention relates to novel nitrogen-containing heterocyclic compounds useful as functional materials (particularly, materials for use in organic electroluminescence devices), a process for producing the same, and an organic electroluminescence device using the same.
Conventionally, a variety of pigments or dyes (e.g., azo-, anthraquinone-, and phthalocyanine-type pigments) have been in use for dying or coloring fiber and others. These pigments or dyes, taken advantage of their characteristic of having a xcfx80-electron conjugate bond within a pigment molecule, have been utilized as, so called, functional pigments. So that these functional pigments have such functions as light-absorptivity (e.g., color, pleochroism), luminous radiation (fluorescent light), photoconductivity, and reversible changes by heat or light (thermochromism, photochromism), these have been used as functional materials in a variety of fields. For example, functional pigments that emit fluorescent light upon irradiation of light are used as fluorescent materials such as fluorescent dyes, fluorescent pigments, fluorescent flaw detecting agents, and fluorescent white dyes. Moreover, pigments that show photochromism have been applied for use in photochromic photos, photochromic materials (light-adjusting materials) for sunglasses, and others. Since photochromic compounds develop colors or fade as their molecular structure changes by the action of light, these compounds have been utilized also as rewritable optical recording materials. These recording materials have high image resolution and thus do not need to be developed in their coloring reaction.
Among these functional pigments mentioned above, in particular, those that emit light by the action (application) of electric fields are useful as emission center compounds for use in organic electroluminescence devices (hereinafter, occasionally abbreviated as organic EL device).
Conventionally, organic electroluminescence devices are composed of a compound or compounds having an electron-transporting function, a hole-transporting function, and an emission center function. There have been reported single-layered ones in which a single layer is provided with all the functions mentioned above, and multi-layered ones in which layers have different functions. Its principle of light emission is considered to be based on the phenomenon that electrons and holes injected from a pair of electrodes recombine within a light-emitting layer to form excitons, exciting an emission center compound forming a light-emitting layer.
Colors that organic EL devices emit can be selected by suitably choosing an emission center compound constituting the light-emitting layer. For example, Japanese Patent Application Laid-Open No. 73443/1996 (JP-A-8-73443) discloses the dimer of pyrazine in which a pyrazine group having a phenyl group is bound to a divalent aromatic group, and an organic EL device containing this pyrazine derivative. However, since this pyrazine dimer emits blue light of which the wavelength is relatively short, the electroluminescence device is limited in its emission wavelength and thus has greatly limited applications.
Thus, it is an object of the present invention to provide a compound capable of emitting light upon irradiation of light or by the action of electric fields and useful as a functional material such as an organic EL device-use material, a process for producing the same, and an organic EL device using the same.
Another object of the present invention is to provide a compound of which the emission wavelength is controllable over a wide range and capable of emitting light of longer wavelength (e.g., yellow to red light), and an organic EL device using the same.
The inventors of the present invention made intensive studies to achieve the above objects and finally found that a specific heterocyclic compound containing a nitrogen atom as a hetero atom emits light upon irradiation of light or by the action of electric fields and therefore is useful as such a functional material as those for organic electroluminescence devices. The present invention was accomplished based on the above findings.
That is, the nitrogen-containing heterocyclic compound of the present invention is represented by the following formula (I) or (II): 
wherein X1 and X2 are the same or different, each representing a hydrogen atom, an alkyl group, or an electron attractive group and at least one of which being an electron attractive group; R1 and R2 are the same or different, each representing a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, or an alkoxy group; and the ring Z is a hydrocarbon ring which may have a substituent or a heterocycle which may have a substituent.
The electron attractive group is at least one member selected from the group consisting of cyano group and acyl groups.
At least X1 or X2 may be a cyano group. R1 and R2 are the groups selected from the group consisting of alkyl groups and aryl groups. The ring Z may be an aromatic ring. The substituent of the ring Z is at least one member selected from the group consisting of alkyl groups, cycloalkyl groups, aryl groups, aralkyl groups, halogens atoms, and hydroxyl group. The compound is capable of emitting light by being irradiated with light. The compound is capable of emitting fluorescent light of which the wavelength is 380 to 800 nm. Moreover, the compound is capable of emitting light by the action of an electric field.
The present invention further includes a process for producing the above-mentioned compound (I) or (II).
The present invention further includes an organic electroluminescence device having, between a pair of electrodes, an organic layer (light-emitting layer) comprising a compound represented by the formula (I) or (II) shown above. The organic layer of this organic electroluminescence device may have (1) a single-layered structure composed of a light-emitting layer having at least one function selected from an electron-transporting function and a hole-transporting function, or (2) a multilayered structure (lamination) composed of a layer having at least one function selected from an electron-transporting function and a hole-transporting function, and a light-emitting layer. Moreover, the organic layer may comprise a compound represented by the above-shown formula (I) or (II) and an organic polymer having at least one function selected from an electron-transporting function and a hole-transporting function.